Unlocking the potential of parboiled rice mill effluent: From microalgae cultivation to bioelectricity production for sustainable development

Rice is a staple food in many Asian countries, and parboiling is a crucial process to reduce grain breakage and improve head rice yield during milling. However, this process generates substantial amounts of nutrient-rich effluent, which, if inadequately treated, leads to environmental issues such as eutrophication. The present review critically examines the parboiling process, highlighting that wastewater contains high concentrations of nitrogen, phosphorus, and organic matter with Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). These nutrients, when utilized effectively, can support sustainable practices such as microalgae cultivation for food and biomass, biofertilizer production, and bioenergy generation, including biofuel and bioelectricity through microbial fuel cells (MFCs). Around 94 % reduction in COD levels and 90 % removal in nitrogen and phosphorus is achieved on effective utilization of nutrients in wastewater for biomass cultivation. Strategies for odor management in parboiling units are also discussed, leveraging techniques such as activated carbon adsorption and advanced oxidation processes adapted from municipal wastewater treatments. The manuscript emphasizes a circular economy approach, proposing integrated solutions for effluent reuse to minimize environmental impact and support sustainable agricultural and energy practices. Future research directions focus on scaling these technologies and optimizing their cost-effectiveness.